Etch profile control of interconnect structures

ABSTRACT

A method of forming a semiconductor structure includes forming an etch stop layer on a substrate, forming a metal oxide layer over the etch stop layer, and forming an interlayer dielectric (ILD) layer on the metal oxide layer. The method further includes forming a trench etch opening over the ILD layer, forming a capping layer over the trench etch opening, and forming a via etch opening over the capping layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 62/491,646, titled “ETCH PROFILE CONTROL OF INTERCONNECTSTRUCTURES,” which was filed on Apr. 28, 2017 and is incorporated hereinby reference in its entirety.

BACKGROUND

With advances in semiconductor technology, there has been increasingdemand for higher storage capacity, faster processing systems, higherperformance, and lower costs. To meet these demands, the semiconductorindustry continues to scale down the dimensions of semiconductordevices, such as metal oxide semiconductor field effect transistors(MOSFETs), including planar MOSFETs and fin field effect transistors(finFETs). Such scaling down has increased the complexity ofsemiconductor manufacturing processes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of this disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the common practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1A is a cross-sectional view of an integrated circuit, inaccordance with some embodiments.

FIG. 1B is a cross-sectional view of an interconnect structure, inaccordance with some embodiments.

FIG. 1C is a cross-sectional view of an interconnect structure.

FIG. 2 is flow diagram of a method for fabricating an interconnectstructure, in accordance with some embodiments.

FIGS. 3-7 are cross-sectional views of an integrated circuit at variousstages of its fabrication process, in accordance with some embodiments.

FIG. 8 is a cross-sectional view of a partially-formed interconnectstructure.

FIGS. 10-12 are cross-sectional views of an integrated circuit atvarious stages of its fabrication process, in accordance with someembodiments.

FIG. 13 is a cross-sectional view of a partially-formed interconnectstructure.

FIG. 14 is a cross-sectional view of an integrated circuit, inaccordance with some embodiments.

Illustrative embodiments will now be described with reference to theaccompanying drawings. In the drawings, like reference numeralsgenerally indicate identical, functionally similar, and/or structurallysimilar elements.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over a second feature in the description that followsmay include embodiments in which the first and second features areformed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Asused herein, the formation of a first feature on a second feature meansthe first feature is formed in direct contact with the second feature.In addition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition does not in itselfdictate a relationship between the various embodiments and/orconfigurations discussed.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like may be used herein for ease of description todescribe an element or a feature's relationship to other element(s) orfeature(s) as illustrated in the figures. The spatially relative termsare intended to encompass different orientations of the device in use oroperation in addition to the orientation depicted in the figures. Theapparatus may be otherwise oriented (rotated 90 degrees or at otherorientations) and the spatially relative descriptors used herein maylikewise be interpreted accordingly.

The fins may be patterned by any suitable method. For example, the finsmay be patterned using one or more photolithography processes, includingdouble-patterning or multi-patterning processes. Double-patterning ormulti-patterning processes can combine photolithography and self-alignedprocesses, allowing patterns to be created that have, for example,pitches smaller than what is otherwise obtainable using a single, directphotolithography process. For example, in some embodiments, asacrificial layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-aligned process. The sacrificial layer isthen removed, and the remaining spacers may then be used to pattern thefins.

It is to be understood that the phraseology or terminology herein is forthe purpose of description and not of limitation, such that theterminology or phraseology of the present specification is to beinterpreted by those skilled in relevant art(s) in light of the presentdisclosure.

As used herein, the term “selectivity” refers to the ratio of the etchrates of two materials under the same etching conditions.

The term “about” as used herein indicates the value of a given quantityvaries by ±10% of the value, unless noted otherwise.

As used herein, the term “substrate” describes a material onto whichsubsequent material layers are added. The substrate itself may bepatterned. Materials added on top of the substrate may be patterned ormay remain unpatterned. Furthermore, the substrate may be a wide arrayof semiconductor materials such as, for example, silicon, germanium,gallium arsenide, indium phosphide, etc. Alternatively, the substratemay be made from an electrically non-conductive material such as, forexample, a glass or a sapphire wafer.

As used herein, the term “high-k” refers to a high dielectric constant.In the field of semiconductor device structures and manufacturingprocesses, high-k refers to a dielectric constant greater than thedielectric constant of SiO₂ (e.g., greater than 3.9).

As used herein, the term “low-k” refers to a small dielectric constant.In the field of semiconductor device structures and manufacturingprocesses, low-k refers to a dielectric constant less than thedielectric constant of SiO₂ (e.g., less than 3.9).

As used herein, the term “p-type” defines a structure, layer, and/orregion as being doped with p-type dopants, such as, for example, boron.

As used herein, the term “n-type” defines a structure, layer, and/orregion as being doped with n-type dopants, such as, for example,phosphorus.

As used herein, the term “vertical” means nominally perpendicular to thesurface of a substrate.

As used herein, the term “critical dimension” refers to the smallestfeature size (e.g., line width) of a finFET and/or an element of anintegrated circuit.

This disclosure provides example methods for improving etch profiles ofback end of the line (BEOL) features, such as vias in interconnectstructures fabricated in the BEOL process of integrated circuit (IC)fabrication. The example methods disclosed herein form vias with etchprofiles more vertical and have smaller ratios between top and bottomopenings of the vias compared to vias formed using other methods. Theseimproved etch profiles of vias help prevent leakage and/or contactbetween the vias and metal lines in the interconnect structures andconsequently improve performance of devices in the integrated circuit.

The IC fabrication process can divided into three stages: front end ofthe line (FEOL), middle of the line (MOL)/middle end of the line (MEOL),and back end of the line (BEOL). In the FEOL stage, functional devicessuch as, for example, field effect transistors (FETs) may be formed. Inthe MOL stage, low level interconnect structures such as, for example,source/drain contact structures and/or gate contact structures of FETsmay be formed to electrically connect the functional devices to highlevel interconnect structures formed in the BEOL stage.

The high level interconnect structures may provide electrical connectionbetween functional devices and/or elements of the IC formed in the FEOLstage. In the BEOL stage, the high level interconnect structures may beformed in an interlayer dielectric (ILD) layer that may be depositedover the IC structure after the MOL stage. The high level interconnectstructure may include two types of conductive structures: verticalinterconnect structures (also referred as “conductive vias” or “vias”)and lateral interconnect structures (also referred as “metal lines”).The conductive vias may run through the BEOL ILD layer in a verticaldirection and may create electrical connections to layers above or belowthe BEOL ILD layer. Metal lines may run through the ILD layer in alateral direction and may connect components within the BEOL ILD layer.The high level interconnect structure may include multiple layers ofconductive vias and metals lines within the BEOL ILD. Each of thesemultiple layers may be separated from adjacent layers by an etch stoplayer except for regions with electrical connections between adjacentlayers.

FIG. 1A is a cross-sectional view of an integrated circuit (IC) 100after the BEOL stage, according to some embodiments. IC 100 may includea substrate 102 and an interconnect structure 104. In some embodiments,substrate 102 may represent one or more functional devices formed in theFEOL stage. The functional devices may have contact structures 122 thatmay be formed in the MOL stage. In some embodiments, interconnectstructure 104 may include layers 104.1 through 104.5. Each of layer104.1 through 104.5 may include an ILD layer 112, conductive vias 110,and metal lines 108. Conductive vias 110 and metal lines 108 may beconfigured to provide electrical connection between the functionaldevices of substrate 102 formed in the FEOL stage.

FIG. 1B is a cross-sectional view of a portion of interconnect structure100, according to some embodiments. As shown in FIG. 1B, conductive via110 may have a substantially vertical profile. The embodiments belowdescribe methods of achieving such vertical via profiles to preventleakage and/or contact between conductive vias and metal line when viaprofiles are tapered as shown in FIG. 1C. Conductive via 110* may beformed other ICs using other methods. Due to the tapered profile ofconductive via 110*, conductive via 110* may short with metal line 108*within region 114 and consequently have a negative impact on theperformance of devices in integrated circuits.

FIG. 14 shows a cross-sectional view of an interconnect structure 1400having conductive vias 1410, according to some embodiments. Conductivevias 1410 may have profiles similar to the substantially verticalprofiles of conductive vias 110 discussed above with reference to FIGS.1A and 1B.

FIG. 2 is a flow diagram of an example method 200 for fabricating aninterconnect structure 1400, shown in FIG. 14, according to someembodiments. Operations can be performed in a different order or notperformed depending on specific applications. It should be noted thatmethod 200 does not produce a complete interconnect structure such asthe structure shown in FIG. 14. Accordingly, it is understood thatadditional processes may be provided before, during, and/or after method200, and that some of the processes are briefly described herein.

For illustrative purposes, the operations illustrated in FIG. 2 will bedescribed with reference to the example fabrication process illustratedin FIGS. 3-7, 10-12, and 14. FIGS. 3-7, 10-12, and 14 arecross-sectional views of interconnect structure 1400 at various stagesof its fabrication, according to some embodiments. A person of ordinaryskill in the art will recognize that the views in FIGS. 3-7, 10-12, and14 are shown for illustration purposes and may not be drawn to scale.According to some embodiments, interconnect structure 1400 may representa portion of interconnect structure 104 discussed with reference to FIG.1A. The above discussion of interconnect structure 104 and itsconductive vias 110, metal lines 108, ILD layer 106, and ESL 112 appliesto the following discussions of conductive vias, metal lines, ILD layer,and ESL with reference to FIGS. 2-7, 10-12, and 14.

In operation 210, an etch stop layer (ESL) is deposited on a substrate.For example, as shown in FIG. 3, ESL 312 may be deposited on substrate302. In some embodiments, substrate 302 may represent a layer of a highlevel interconnect structure having metal lines 322 to which conductivevias 1410 of interconnect structure 1400 (shown in FIG. 14) may beelectrically connected. In some embodiments, substrate 302 may representone or more functional devices formed in the FEOL stage. The functionaldevices may have contact structures 322, formed in the MOL stage, towhich conductive vias 1410 of interconnect structure 1400 may beelectrically connected. In some embodiments, substrate 302 may representa semiconductor material such as, but not limited to, silicon havingconductive structures 322 to which conductive vias 1410 of interconnectstructure 1400 may be electrically connected.

In some embodiments, substrate 302 may include a crystalline siliconsubstrate (e.g., wafer). In some embodiments, substrate 302 may include(i) an elementary semiconductor such as, for example, germanium; (ii) acompound semiconductor including silicon carbide, gallium arsenide,gallium phosphide, indium phosphide, indium arsenide, and/or indiumantimonide; (iii) an alloy semiconductor including silicon germaniumcarbide, silicon germanium, gallium arsenic phosphide, gallium indiumphosphide, gallium indium arsenide, gallium indium arsenic phosphide,aluminum indium arsenide, and/or aluminum gallium arsenide; or (iv) acombination thereof. Further, substrate 302 may be doped depending ondesign requirements (e.g., p-type substrate or n-type substrate). Insome embodiments, substrate 302 may be doped with p-type dopants (e.g.,boron, indium, aluminum, or gallium) or n-type dopants (e.g., phosphorusor arsenic). Based on the disclosure herein, a person of ordinary skillin the art will recognize that other materials for substrate 302 arewithin the scope and spirit of this disclosure.

In some embodiments, conductive structures 322 may include a suitableconductive material such as, for example, Ti (titanium), tungsten (W),copper (Cu), cobalt (Co), nickel (Ni), silver (Ag), Al, titaniumaluminum nitride (TiAIN), tantalum carbide (TaC), tantalum carbo-nitride(TaCN), tantalum silicon nitride (TaSiN), manganese (Mn), Zr, titaniumnitride (TiN), tantalum nitride (TaN), ruthenium (Ru), molybdenum (Mo),tungsten nitride (WN), titanium carbide (TiC), titanium aluminum carbide(TiAlC), tantalum aluminum carbide (TaAIC), metal alloys, and/orcombinations thereof. Based on the disclosure herein, a person ofordinary skill in the art will recognize that other materials forconductive structures 322 are within the scope and spirit of thisdisclosure.

ESL 312 may be configured to protect substrate 312 and conductivestructures 322 during, for example, formation of interconnect structure1400. In some embodiments, ESL 312 may include, for example, siliconnitride (SiN_(x)), silicon oxide (SiO_(x)), silicon oxynitride (SiON),silicon carbide (SiC), silicon carbo-nitride (SiCN), boron nitride (BN),silicon boron nitride (SiBN), silicon carbon boron nitride (SiCBN), or acombination thereof. In some embodiments, ESL 312 may include siliconnitride or silicon oxide formed by low pressure chemical vapordeposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD),chemical vapor deposition (CVD), atomic layer deposition (ALD), orsilicon oxide formed by a high-aspect-ratio process (HARP). In someembodiments, ESL 312 may have a thickness 312 t in a range from about 1nm to 3 nm. Based on the disclosure herein, a person of ordinary skillin the art will recognize that other materials, formation methods, andthicknesses for ESL 312 are within the scope and spirit of thisdisclosure.

In some embodiments, a liner 316 having oxygen doped carbide materialmay be deposited on ESL 312. In some embodiments, liner 316 has athickness 316 t in a range from about 3 nm to about 8 nm and may be usedas another etch stop layer. In some embodiments, liner 316 may be formedby LPCVD, PECVD, or CVD.

In referring to FIG. 2, in operation 220, a metal oxide layer and aninterlayer dielectric (ILD) layer is deposited over the ESL. Forexample, as shown in FIG. 3, a metal oxide layer 318 may be deposited onlayer 316, followed by a deposition of an ILD layer 320 on metal oxidelayer 318. Metal oxide layer 318 may help improve the etch profile ofthe vias as will be discussed in further detail below. In someembodiments, metal oxide layer 318 may include oxides of a suitablemetal such as, for example, chromium (Cr), Al, Ti, tin (Sn), zinc (Zn),magnesium (Mg), silver (Ag), Ni, Mo, or a combination thereof. Metaloxide layer 318 may be deposited using a suitable metal oxide depositionprocess such as, for example CVD.

In some embodiments, a layer having metal nitride or metal carbide maybe used instead of metal oxide layer 318. In some embodiments, a stackof one or more layers having metal oxide, metal nitride, metal carbide,or a combination thereof may be used in place of metal oxide layer 318for the fabrication of interconnect structure 1400 (shown in FIG. 14).

ILD layer 320 may be similar in structure and function to ILD layers 106of interconnect structure 104 discussed above with reference to FIG. 1A.In some embodiments, ILD layer 320 may include a low-k dielectricmaterial. Low-k materials may have a dielectric constant below 3.9.Low-k materials in ILD layer 320 may help reduce unwanted parasiticcapacitances and minimize resistance-capacitance (RC) delays. In someembodiments, ILD layer 320 may be formed by a suitable dielectricdeposition process such as, for example, CVD or ALD. ILD layer 320 mayhave a thickness 320 t in a range from about 90 nm to about 150 nm. ILDlayer 320 may help provide electrical isolation between adjacentconductive vias 1410 and/or adjacent metal lines 1408 of interconnectstructure 1400 that may be formed in ILD layer 320. Conductive vias 1410may run vertically along, for example, Z-axis in ILD layer 320 and metallines 1408 may run laterally along, for example, Y-axis in ILD layer320.

As shown in FIG. 3, the deposition of ILD layer 320 may be followed by adeposition of a stack of masking layers. The stack of masking layers mayinclude a nitrogen free anti-reflective layer (NFARL) 324, a first hardmask layer 326, and a second hard mask layer 328. NFARL 324 may helpprotect ILD layer 320 during subsequent patterning of first and secondhard mask layers 326 and 328. The patterning of first and second hardmask layers 326 and 328 may involve chlorine based processes that mayetch ILD layer 320 if not protected by a masking layer such as, forexample, NFARL 324. In some embodiments, NFARL 324 may include adielectric material and may be formed using a suitable deposition methodsuch as, for example, CVD. In some embodiments, a gas mixture includingsilane and carbon dioxide may be used in the deposition of NFARL 324.NFARL may have a thickness 324 t in a range from about 20 nm to about 30nm.

In some embodiments, first hard mask layer 326 may be deposited using,for example, PVD and may include silicon nitride, titanium nitride, or acombination thereof. First hard mask layer 326 may have a thickness 326t in a range from about 25 nm to about 40 nm. Second hard mask layer 328may include tetraethoxysilane (TEOS) formed by, for example, CVD,according to some embodiments. Second hard mask layer 328 may have athickness 328 t in a range from about 25 nm to about 40 nm.

In referring to FIG. 2, in operation 230, hard mask layers over the ILDlayer are patterned. For example, as shown in FIG. 4, first and secondhard mask layers 326 and 328 may be patterned to form trench etchopenings 430, 432, and 434. These trench etch openings may define theareas for the formation of subsequent trenches in ILD layer 320. Thesetrenches may subsequently form metal lines 1408 of interconnectstructure 1400 (FIG. 14) as described in further detail below. Thewidths W₁, W₂, and W₃ of respective trench etch openings 430, 432, and434 may define the widths of trenches formed in ILD layer 320 insubsequent processing. Patterning of first and second hard mask layers326 and 328 may be performed by photolithography and a dry etchingprocess. In some embodiments, the dry etch process may be chlorine basedprocess.

In referring to FIG. 2, in operation 240, vias and trenches are formedin the ILD layer. For example, as shown through FIGS. 5-7 and 9-12, vias1250 and 1252 and trenches 1230, 1232, and 1234 may be formed in ILDlayer 320. In some embodiments, as shown in FIG. 5, a stack of layersmay be deposited on the structure of FIG. 4. The stack of layers mayinclude first and second organic layers 536 and 544, a low temperatureoxide (LTO) layer 538, first and second Si-based layers 540 and 546, acapping layer 542, and a photoresist layer 548. Each of these layers ofthe stack of layers may be arranged in the order shown in FIG. 5,according to some embodiments. This stack of layers may help form viaetch openings 650, 652, 750, and 752 (as shown in FIGS. 6-7) that maydefine the areas for subsequent formation of vias 1250 and 1252 (shownin FIG. 12) in ILD layer 320. This stack of layers may also help controlthe etch profiles of vias 1250 and 1252 during their formation.

In some embodiments, first and second organic layers 536 and 544 may beformed in a similar process such as, for example, by spin coating asuitable polymer material on the structure of FIG. 4 and on cappinglayer 542, respectively, at a temperature ranging from about 100° C. toabout 300° C. First and second polymer layers may have a respectivethickness 536 t and 542 t in a range from about 150 nm to about 300 nm.

LTO layer 538 may include silicon oxide formed by, for example, CVDusing a gas mixture having silane and oxygen, according to someembodiments. LTO layer 538 may be deposited at a low temperature rangingfrom about 50° C. to about 200° C. LTO layer 538 may have a thickness538 t in a range from about 10 nm to about 30 nm.

First and second Si-based layers 540 and 546 may include differentmaterials and may be formed in different deposition processes, accordingto some embodiments. First Si-based layer 540 may be formed by, forexample, CVD or PVD using a gas mixture having elements of silicon,oxygen, and carbon. In some embodiments, first Si-based layer 540 mayhave a thickness 540 t in a range from about 10 nm to about 30 nm.Second Si-based layer 546 may be deposited, for example, by spin-coatingsiloxane on second organic layer 544 at a temperature ranging from about50° C. to about 200° C. In some embodiments, second Si-based layer 546may have a thickness 546 t in a range from about 30 nm to about 40 nm.In some embodiments, first and second Si-based layers 540 and 546 mayinclude same material.

In some embodiments, capping layer 542 may include silicon oxide formedby, for example, CVD using a gas mixture having silane and oxygen at atemperature ranging from about 200° C. to about 500° C. Capping layer542 may have a thickness 542 t in a range from about 30 nm to about 40nm.

Following the deposition of the stack of layers on the structure of FIG.4, photoresist layer 548 may be patterned to form a first pair of viaetch openings 650 and 652 as shown in FIG. 6. This formation is followedby one or more etching processes to etch second Si-based layer 546 andsecond organic layer 544 through first pair of via etch openings 650 and652 to form a second pair of via etch openings 750 and 752 as shown inFIG. 7. In some embodiments, second Si-based layer 546 may be etched ina dry etch process (e.g., reactive ion etching process) using a gasmixture having fluorocarbon (C_(x)F_(y)), nitrogen, and argon. The gasmixture may have about 10% to about 70% C_(x)F_(y). The flow rate ofC_(x)F_(y) may range from about 100 sccm to about 400 sccm and the flowrate of nitrogen and argon may range from about 50 sccm to about 300sccm. The etch process may be carried out for a period of time rangingfrom about 10 sec to about 90 sec at a temperature ranging from about10° C. to about 90° C., under a pressure ranging from about 15 mTorr toabout 100 mTorr.

In some embodiments, second organic layer 544 may be etched in a dryetch process (e.g., reactive ion etching process) using a gas mixturehaving hydrogen, nitrogen, and argon. The gas mixture may have about 5%to about 20% hydrogen. The flow rate of hydrogen may range from about 20sccm to about 100 sccm and the flow rate of nitrogen and argon may rangefrom about 100 sccm to about 400 sccm. The etch process may be carriedout for a period of time ranging from about 10 sec to about 90 sec at atemperature ranging from about 10° C. to about 90° C., under a pressureranging from about 15 mTorr to about 100 mTorr.

After the etching of second Si-based layer 546 and second organic layer544 through via etch openings 650 and 652, the patterns of via etchopenings 650 and 652 may have transferred within second organic layer546. Due to the presence of second Si-based layer 546, the widths of thetransferred etched patterns (not shown) in second organic layer 544 maybe smaller than widths 650 w and 652 w. This may be due to deposition ofsilicon fluoride based material on sidewalls of via etch openings (notshown) formed in second Si-based layer 546 during its etching process.And as a result, the widths of the via etch openings in second Si-basedlayer 546 through which second organic layer 544 is etched may benarrower than widths 650 w and 652 w. Thus, second Si-based layer 546may help shrink the widths of subsequent vias 1250 and 1252 of FIG. 12formed in ILD layer 320 compared to the widths of via etch openings 650and 652 patterned in photoresist layer 548.

Following the etch of second organic layer 544, capping layer 542, firstSi-based layer 540, and LTO layer 538 may be etched to form second pairof via etch openings 750 and 752, as shown in FIG. 7. In someembodiments, capping layer 542 may be etched in a dry etch process(e.g., reactive ion etching process) using C_(x)F, gas having a flowrate ranging from about 100 sccm to about 400 sccm. The etch process maybe carried out for a period of time ranging from about 10 sec to about90 sec at a temperature ranging from about 10° C. to about 90° C., undera pressure ranging from about 15 mTorr to about 100 mTorr. This etchprocess transfers the via etch openings (not shown) from second organiclayer 544 to capping layer 542. During the etch of capping layer 542,second Si-based layer 546 and second organic layer 544 may be etched offfrom top surface of capping layer 542.

In some embodiments, the stack of layers of FIG. 5 discussed above maynot include second organic layer 544 and second Si-based layer 546.Instead, photoresist layer 548 may be deposited on capping layer 542. Inthis embodiment, the etching of capping layer 542 may be followed by theformation of via etch opening 650 and 652.

First Si-based layer 540 and LTO layer 538 may be etched through thetransferred via etch openings (not shown) in capping layer 542. In someembodiments, first Si-based layer 540 may be etched in a dry etchprocess (e.g., reactive ion etching process) using a gas mixture havingC_(x)H_(y)F_(z) gas, oxygen, nitrogen, and argon. The gas mixture mayhave about 5% to about 10% C_(x)H_(y)F_(z) and about 1% to about 5%oxygen. The flow rates of C_(x)H_(y)F_(z) may range from about 5 sccm toabout 100 sccm, of oxygen may range from about 5 sccm to about 30 sccm,and of nitrogen and argon may range from about 50 sccm to about 300sccm. The etch process may be carried out for a period of time rangingfrom about 10 sec to about 90 sec at a temperature ranging from about10° C. to about 90° C., under a pressure ranging from about 15 mTorr toabout 100 mTorr.

In some embodiments, LTO layer 538 may be etched in a dry etch process(e.g., reactive ion etching process) using a gas mixture havingfluorocarbon (CF_(y)), nitrogen, and argon. The gas mixture may haveabout 1% to about 20% C_(x)F_(y). The flow rates of C_(x)F_(y) may rangefrom about 10 sccm to about 30 sccm and of nitrogen and argon may rangefrom about 600 sccm to about 1500 sccm. The etch process may be carriedout for a period of time ranging from about 10 sec to about 90 sec at atemperature ranging from about 10° C. to about 90° C., under a pressureranging from about 15 mTorr to about 100 mTorr.

As shown in FIG. 7, during the etch of first Si-based layer 540 and LTOlayer 538, capping layer 542 may be etched off from top surface of firstSi-based layer 540. Widths 750 w and 752 w of second pair of via etchopenings 750 and 752 may be narrower than widths 650 w and 652 w becauseof narrower widths of the transferred via etch openings in secondorganic layer 544, as discussed above.

Presence of capping layer 542 may help achieve substantially verticaletch profiles in via etch openings 750 and 752 compared to etch profilesin via etch openings 750* and 752* (as shown in FIG. 8) formed in amethod without using a capping layer such as capping layer 542. AnglesA₁ and A₂ in etch profiles of respective via etch openings 750 and 752are larger than angles A₃ and A₄ in etch profiles of respective via etchopenings 750* and 752*. In some embodiments, A₁ and A₂ may be in a rangefrom about 83° to about 90°, and A₃ and A₄ may be in a range from about65° to about 70°. Angles A₁ and A₂ may be the angles between therespective sidewalls of via etch openings 750 and 752 and X-axis. AnglesA₃ and A₄ may be the angles between the respective sidewalls of via etchopenings 750* and 752* and X-axis. Hence, substantially vertical etchprofiles of via etch openings 750 and 752 may be achieved with the helpof capping layer 542 because capping layer 542 helps protect firstSi-based layer 540 on LTO layer 538 during their etch processes. FirstSi-based layer 540 helps prevent over etching of LTO layer 538 in thelateral direction (e.g., X-direction). As shown in FIG. 8, firstSi-based layer 540 is etched off during formation of via etch openings750* and 752* in LTO layer 538.

Achieving substantially vertical etch profiles in via etch openings mayresult in similar etch profiles of vias 1250 and 1252 (FIG. 14)subsequently formed in ILD layer 320. As discussed above, substantiallyvertical etch profiles of vias may help prevent leakage and/or contactbetween the vias and metal lines in interconnect structures.

The formation of via etch openings 750 and 752 may be used to formpartial vias 950 and 952 in ILD layer 320 as shown in FIG. 9. Thesepartial vias 950 and 952 may be formed after etching first organic layer536, NFARL 324 and ILD layer 320 through via etch openings 750 and 752.In some embodiments, first organic layer 536 may be etched in a processsimilar to the etching process of second organic layer 544. During thisetching process, via etch openings (not shown) having similar profilesas via etch openings 750 and 752 may be formed in first organic layer536 and first Si-based layer 540. LTO layer 538 may be etched off thetop surface of first organic layer 536 during this etching process.

NFARL layer 342 and ILD layer 320 are then etched through the via etchopenings formed in first organic layer 536. In some embodiments, NFARLlayer 342 and ILD layer 320 may be etched in a dry etch process (e.g.,reactive ion etching process) using a gas mixture having C_(x)F_(y) gas,oxygen, nitrogen, and argon. The gas mixture may have about 5% to about10%/o C_(x)F_(y) and about 1% to about 5% oxygen. The flow rates ofC_(x)F_(y) may range from about 10 sccm to about 60 sccm, of oxygen mayrange from about 5 sccm to about 30 sccm, and of nitrogen and argon mayrange from about 5 sccm to about 1000 sccm. The etch process may becarried out for a period of time ranging from about 10 sec to about 90sec at a temperature ranging from about 10° C. to about 90° C., under apressure ranging from about 15 mTorr to about 100 mTorr.

After the formation of partial vias 950 and 952, first organic layer 536may be removed from the top surfaces of first hard mask layer 328 andNFARL 324. The removal of first organic layer 536 may be followed bycontinued etch of ILD layer 320 to extend partial vias 950 and 952 tothe top surface of metal oxide layer 318, as shown in FIG. 10. Duringthe continued etch of ILD layer 320, first hard mask layer 328 and NFARLlayer 342 are etched to form partial trenches 1030, 1032, and 1034, asshown in FIG. 10. The widths W₄, W₅, and W₆ of respective partialtrenches 1030, 1032, and 1034 may be defined by widths W₁, W₂, and W₃ ofrespective trench etch openings 430, 432, and 434 discussed above. Insome embodiments, trench width W₄ may be in a range from about 85 nm toabout 100 nm and trench height H₁ may be in a range from about 50 nm toabout 80 nm.

In some embodiments, after the formation of partial trenches 1030, 1032,and 1034, second hard mask layer 326 and portions of metal oxide layer318 exposed through partial vias 950 and 952 may be removed. The secondmask layer 326 and the exposed portions of metal oxide layer 318 may beremoved by, for example, a wet etching process using hydrogen peroxideat a temperature ranging from about 30° C. to about 10° C. The etch rateduring this wet etch process may be in a range from about 0.2 nm/sec toabout 0.5 nm/sec.

The removal of second mask layer 326 and the portions of metal oxidelayer 318 may be followed by etching of remaining portions of NFARL 324on ILD layer 320 and portions of liner 316 exposed through partial vias950 and 952. Such etching may result in the formation of trenches 1230,1232, and 1234 and vias 1250 and 1252 as shown in FIG. 12. In someembodiments, this etching may be performed in a dry etch process (e.g.,reactive ion etching process) using a gas mixture having C_(x)F_(y) gas,oxygen, carbon dioxide, nitrogen, and argon. The gas mixture may haveabout 1% to about 5% C_(x)F_(y), about 1% to about 5% oxygen, and about1% to about 5% carbon dioxide. The etch process may be carried out at atemperature ranging from about 20° C. to about 60° C., under a pressureranging from about 15 mTorr to about 100 mTorr. In some embodiments,portions of ESL 312 may be etched to open vias 1250 and 1252 toconductive structures 322.

FIG. 13 shows tapered profiles of vias 1250* and 1252* formed in amethod without using a metal oxide layer such as metal oxide layer 318.The presence of metal oxide layer 318 may help achieve the substantiallyvertical profiles of vias 1250 and 1252. Angles A₅ and A₆ in profiles ofrespective vias 1250 and 1252 are larger than angles A₇ and A₈ inprofiles of respective vias 1250* and 1252*. In some embodiments, A₅ andA₆ may be in a range from about 70° to about 80°, and A₇ and A₈ may bein a range from about 50° to about 60°. Angles A₇ and A₈ may be anglesbetween the respective sidewalls of vias 1250 and 1252 and X-axis.Angles A₇ and A₈ may be the angles between the respective sidewalls ofvias 1250* and 1252* and X-axis.

In some embodiments, via 1250 may have a top width W₇ to bottom width W₈ratio in a range from about 2 to about 3 and via 1250* may have a topwidth W₉ to bottom width W₁₀ ratio in a range from about 3 to about 4,which is larger than that of via 1250. In some embodiments, via 1250 mayhave a bottom width W₈ to height H₂ ratio in a range from about 45 toabout 55 and via 1250* may have a bottom width W₁₀ to height H₃ ratio ina range from about 55 to about 65, which is larger than that of via1250. In some embodiments, via 1250 may have a height H₂ to top width W₇ratio in a range from about 65 to about 75 and via 1250* may have aheight H₃ to top width W₉ ratio in a range from about 40 to about 50,which is smaller than that of via 1250. Hence, compared to the profileof via 1250, via 1250 has a tapered via profile.

In referring to FIG. 2, in operation 250, conductive material isdeposited in the vias and trenches to form conductive vias and metallines. For example, as shown in FIG. 14, conductive vias 1410 and metallines 1408 of interconnect structure 1400 are formed. Formation ofconductive vias 1410 and metal lines 1408 may involve depositingconductive materials such as, for example, W, Al, Co, Cu, or a suitableconductive material in vias 1250 and 1252 and in trenches 1230, 1232,and 1234 using, for example, PVD, CVD, or ALD, according to someembodiments.

The above embodiments describe methods for achieving substantiallyvertical profiles of vias (e.g., vias 1250 and 1252) of interconnectstructures (e.g., interconnect structure 1400). Achieving substantiallyvertical profiles of the vias may help prevent leakage and/or contactbetween the vias and metal lines in interconnect structures. In someembodiments, the use of an oxide capping layer (e.g., capping layer 542)during the formation of via etch openings (e.g., via etch openings 750and 752) helps achieve substantially vertical etch profiles of the viaetch openings, which in turn helps achieve substantially verticalprofiles of the vias. In some embodiments, the presence of a metal oxidelayer below the ILD layer of the interconnect structure helps form asubstantially vertical profile of the vias compared to vias formed inmethod without using a metal oxide layer. For example, a via formedusing a metal oxide layer in the interconnect structure can have a viaprofile sidewall that makes an angle with a horizontal axis in a rangefrom about 70° to about 80°. This angle is larger than the angle made bya via profile sidewall of a via formed without a metal oxide layer,which can be in a range from about 50° to about 60°. Some of theembodiments are described below.

In some embodiments, a method of forming a semiconductor structureincludes forming an etch stop layer on a substrate, forming a metaloxide layer over the etch stop layer and forming an interlayerdielectric (ILD) layer on the metal oxide layer. The method furtherincludes forming a trench etch opening over the ILD layer, forming acapping layer over the trench etch opening, and forming a via etchopening over the capping layer.

In some embodiments, a method of forming an interconnect structureincludes forming an etch stop layer on a substrate, forming a metaloxide layer over the etch stop layer, and forming an interlayerdielectric (ILD) layer on the metal oxide layer. The method furtherincludes forming a low temperature oxide layer over the ILD layer,forming a capping layer over the low temperature oxide layer, andforming a via etch opening in the capping layer.

In some embodiments, a method of forming an interconnect structureincludes forming an etch stop layer on a substrate, forming a metaloxide layer over the etch stop layer, and forming an interlayerdielectric (ILD) layer on the metal oxide layer. The method furtherincludes forming a first conductive structure extending along a firstdirection in the ILD layer and forming a second conductive structureextending along a second direction in the ILD layer and in the metaloxide layer. The second direction is perpendicular to the firstdirection.

In some embodiments, an interconnect structure includes an etch stop ona substrate, a metal oxide layer positioned over the etch stop layer, aninterlayer dielectric (ILD) layer positioned on the metal oxide layer,and a conductive structure in the ILD layer. The conductive structure ispositioned in the metal oxide layer and in the etch stop layer.

In some embodiments, an integrated circuit includes a semiconductordevice and an interconnect structure. The semiconductor device includescontact structures and the interconnect structure is coupled to thecontact structures. The interconnect structure includes an etch stoplayer positioned over the semiconductor device, a metal oxide layerpositioned over the etch stop layer, an interlayer dielectric (ILD)layer positioned on the metal oxide layer, and a conductive viapositioned within the metal oxide layer and the ILD layer.

In some embodiments, a semiconductor structure includes an etch stoplayer positioned over a substrate, a metal oxide layer positioned overthe etch stop layer, and an interlayer dielectric (ILD) layer positionedon the metal oxide layer. The semiconductor structure further includes afirst conductive structure extending along a first direction in the ILDlayer and a second conductive structure extending along a seconddirection in the ILD layer and in the metal oxide layer. The seconddirection is perpendicular to the first direction.

The foregoing disclosure outlines features of several embodiments sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodimentsintroduced herein. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

1. A method of forming an interconnect structure, the method comprising:forming an etch stop layer on a substrate; forming a metal oxide layerover the etch stop layer; forming an interlayer dielectric (ILD) layeron the metal oxide layer; forming a low temperature oxide layer over theILD layer; forming a capping layer over the low temperature oxide layer;and forming a via etch opening in the capping layer.
 2. The method ofclaim 1, wherein the forming the via etch opening in the capping layercomprises: depositing a photoresist layer on the capping layer; andetching the capping layer through a pattern in the photoresist layer. 3.The method of claim 1, further comprising: forming a via in the ILDlayer and on the metal oxide layer; and etching a portion of the metaloxide layer through the via.
 4. The method of claim 3, furthercomprising depositing a conductive material in the via.
 5. The method ofclaim 3, wherein a sidewall of the via forms an angle with a horizontalaxis in a range from about 70° to about 80°.
 6. The method of claim 1,wherein the capping layer comprises oxide material.
 7. The method ofclaim 1, wherein the metal oxide layer comprises chromium, aluminum,titanium, tin, zinc, magnesium, or silver.
 8. A method of forming asemiconductor structure, the method comprising: forming an etch stoplayer on a substrate; forming a metal oxide layer over the etch stoplayer; forming an interlayer dielectric (ILD) layer on the metal oxidelayer; forming a trench etch opening over the ILD layer; forming acapping layer over the trench etch opening; and forming a via etchopening over the capping layer.
 9. The method of claim 8, furthercomprising forming a low temperature oxide layer between the cappinglayer and the trench etch opening.
 10. The method of claim 8, furthercomprising forming first and second silicon-based layers over the trenchetch opening and over the capping layer, respectively.
 11. The method ofclaim 8, further comprising forming first and second organic layers overthe trench etch opening and over the capping layer, respectively. 12.The method of claim 8, wherein the forming the trench etch openingcomprises: depositing a nitrogen-free dielectric layer on the ILD layer;and patterning a silicon-based layer and a nitride layer on thenitrogen-free dielectric layer.
 13. The method of claim 8, furthercomprising: forming a low temperature oxide layer over the trench etchopening; and forming another via etch opening in the low temperatureoxide layer, the another via etch opening having a width smaller than awidth of the via etch opening.
 14. The method of claim 8, wherein thecapping layer comprises an oxide material.
 15. The method of claim 8,further comprising forming a via in the ILD layer and the metal oxidelayer.
 16. The method of claim 8, further comprising forming a via inthe ILD layer, the metal oxide layer, and the etch stop layer.
 17. Themethod of claim 8, wherein the metal oxide layer comprises chromium,aluminum, titanium, tin, zinc, magnesium, or silver. 18-20. (canceled)21. A method, comprising: depositing a stack over a substrate, whereinthe stack comprises: an etch stop layer over the substrate; anoxygen-doped carbide layer over the etch stop layer; and ametal-containing layer over the oxygen-doped carbide layer; depositing adielectric layer over the stack; etching the dielectric layer and thestack to form an opening, wherein a sidewall angle of the opening isless than about 70°.
 22. The method of claim 21, further comprising:disposing a first organic layer over the dielectric layer; depositing another stack over the organic layer, wherein the other stack comprises:an oxide layer; a silicon-based layer; and a capping layer, comprisingsilicon oxide, over the silicon-based layer; depositing a second organiclayer over the other stack; and etching the second organic layer and theother stack to form an other opening, wherein a sidewall angle of theother opening is less than about 83°.
 23. The method of claim 21,wherein the metal-containing layer comprises chromium oxide, aluminumoxide, titanium oxide, tin oxide, zinc oxide, magnesium oxide, silveroxide, nickel oxide, molybdenum oxide, or combinations thereof.